Soft and stretchable textile fabrics made from polytrimethylene terephthalate

ABSTRACT

In this invention, we found unexpectedly that when PTT fiber is drawn,textured and set under certain conditions, the fabrics made from textured fibers by this texturing process possess stretch and hand which is much better than current commercially available PBT and PET stretch fabrics, and better than PTT textured fibers made under similar conditions without the setting step. Specifically, the invention describes the spinning of PTT polymer into yarn with an elongation of 60 to 160% and draw-texturing the yarn using a false-twist draw-textured yarn machine at a draw ratio of 1.02 to 1.6 and a yarn temperature of 120 to 160° C., preferably 130 to 150° C. The yarn is further set, usually with a secondary heater, at a yarn temperature of 70 to 130° C., preferably 85 to 115° C., prior to winding. Then knitted fabrics are dyed, tentor-set, and finished with fabric softener. This invention is different from the above teachings in that the PTT yarn is draw-textured in a false-twist machine. The yarn is crimped (textured) at a much lower first heater temperature of 130 to 160° C. than described in the above prior art, is set with a secondary heater at 70 to 130° C. Fabrics made from the set yarn have as good or better stretch and better hand than fabrics made from the un-set yarn.

FIELD OF THE INVENTION

[0001] This invention relates to 1,3-propanediol-based polyesters such as polytrimethylene terephthalate which are used to make textile fabrics and. More particularly, the invention relates to a new polytrimethylene terephthalate textile fabrics which exhibit very good stretch and very good hand.

BACKGROUND OF THE INVENTION

[0002] Stretch and hand are two highly desirable tactile properties for textile fabrics. Hand is the term used in the textile industry to describe the tactile qualities of a fabric, e.g., softness, firmness, elasticity, fineness, resilience, and other qualities perceived by touch. Stretch fabrics are typically made from (1) fibers with good elastic recovery such as nylons and polybutylene terephthalate (PBT), or (2) a mixture of typical nylon or polyester yarns and an elastic fiber such as the polyurethane elastomer Spandex. Soft hand derives partly from the intrinsic property of the polymer such as modulus and also from the yarn and fabric processing such as setting the yarn during draw-texturing and mercerizing the fabric with caustic sodium hydroxide solution.

[0003] Therefore, stretch and soft hand can be manipulated to some extent. However, improvement in one usually is accompanied by a negative effect on the other. For example, fiber stretch can be improved by increasing its crimp level or bulk and latent torque energy during draw-texturing, by increasing the yarn count and denier per filament (dpf), or by pre-twisting the yarn followed by texturing. However, the increase in stretch is achieved at the expense of hand. Higher crimp yarn and higher dpf fabrics feel coarse and have poorer hand. The most common way to improve the hand of a draw textured yarn (DTY) is to set the yarn using a secondary heater at a temperature usually lower than the temperature at which crimping is carried out (in the first or primary heater). This secondary heat set treatment turns the yarn into a set DTY. Although the hand is improved, the secondary setting process also removes some of the crimp and latent torque energy resulting in poorer stretch (see Lubos Hes and Petr Ursiny, Yarn Texturing Technology, Comett Eurotex, 1994 and Ali Demir, Hassan Mohamed Behery, Synthetic Filament Yarn: Texturing Technology,Prentice Hall, 1997, on the technology of producing high extensibility and low extensibility yarns)..

[0004] It is therefore difficult to obtain fibers or fabrics that have both good stretch and good hand without using elastic fibers such as Spandex. The only fiber currently that comes close to achieving the combination of good stretch and hand is PBT polyester. It is marketed by various fiber companies such as Hoechst-Celanese as extra stretch performance fiber. However, it is difficult to set PBT textured yarn because of its low glass transition temperature.

[0005] PTT fiber is known to have good elastic recovery and soft hand because of its low modulus. British patent no. 1254826, Japanese application 09078373, and WO patent application 00/22210 teach the spinning and texturing of PTT yarns for applications in carpets and stretch fabrics in sportswear, leisure wears, etc. The texturing of the yarns were done either by air texturing or false-twist texturing. Japanese application 09078373 teaches texturing of PTT yarns by manipulating the texturing heater temperature between 165 and 180° C. such that the textured yarn has a Young modulus <30 g/den to maintain a soft hand. WO patent application 00/22210 teaches that PTT fiber with a modulus, Q, and an elastic recovery, R, such that the ratio of Q/R satisfies the relationship of 0.18<=Q/R<=0.45, is useful for making textile fabrics. The Q/R ratio is merely a re-statement of teachings found in British patent no. 1254826 and Japanese application 09078373. None of the above references disclose further setting the textured yarn with a secondary heater.

[0006] They also used modulus as a measure of soft hand. Although hand is related to yarn modulus it is a much more complicated tactile property. It encompasses softness without feeling limpy, drapability, dry touch, and fabric fullness to touch. Although a robotic instrument (Kawabata Evaluation System) was developed to measure fabric hand, it has its advantages and drawbacks in simulating human touch. Therefore, touch by experienced textile personnel is still widely used to evaluate the hand of fabrics as in Japanese application 09078373. In this patent application, example 5 and its comparative example have Young moduli of 21 and 20 g/den., respectively, yet the hand of the example 5 was rated at 7 while the later was rated 5 on a scale of 1 to 8., 8 being the best and 1 being the worst. This shows that low modulus, although is a reasonable measure, is inadequate in evaluating hand.

BRIEF SUMMARY OF THE INVENTION

[0007] In this invention, we found unexpectedly that when PTT fiber is drawn and textured under certain conditions, the fibers and fabrics made from this texturing process possess stretch and hand which is much better than current commercially available PBT and PET stretch fabrics. Specifically, the invention describes the spinning of PTT polymer into a partially oriented yarn (POY) and draw-texturing the POY using a false-twist draw-textured yarn machine at a draw ratio of 1.02 to 1.6, preferably between 1.05 to 1.4, and a yarn temperature of 120 to 160° C., preferably 130 to 150° C. Alternatively, the soft stretch yarn made be made by spinning a polytrimethylene terephthalate polymer yarn and drawing it in-situ using heated godets to a final elongation of 60 to 150% at the same temperature. The yarn is further set, usually with a secondary heater, at a yarn temperature of 70 to 130° C., preferably 85 to 115° C., prior to winding. Then knitted fabrics are dyed, tentor-set, and finished with fabric softener. This invention is different from the above teachings in that the PTT partially oriented yarn is draw-textured in a false-twist machine. The yarn is crimped (textured) at a much lower first heater temperature of 130 to 160° C. than described in the above prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0008] The polytrimethylene terephthalate polymer is prepared by the reaction of a molar excess of 1,3-propanediol (PDO) and terephthalic acid (TPA) (or dimethyl terephthalate) by esterification followed by polycondensation, with the important proviso that the reaction conditions include maintenance of relatively low concentration of PDO and TPA in the melt reaction mixture.

[0009] As used herein, “1,3-propanediol-based aromatic polyester” refers to a polyester prepared by the condensation polymerization reaction of one or more diols with one or more aromatic diacids or alkyl esters thereof (herein referred to collectively as “diacid”) in which at least 80 mole percent of the diol(s) is 1,3-propanediol. “Polytrimethylene terephthalate” refers to such a polyester in which at least about 80 mole percent of the diacid(s) is terephthalic acid. Other diols which may be copolymerized in such a polyester include, for example, ethylene glycol, diethylene glycol, 1,4-cyclohexane dimethanol, and 1,4-butanediol; and other aromatic and aliphatic acids which may be copolymerized include, for example, isophthalic acid and 2,6-naphthalane dicarboxylic acid.

[0010] The preparation of the invention composition can be conveniently described by reference to an esterification step, a prepolymerization step, and a polycondensation step. The process can be carried out in batch or continuous mode. Each step can be carried out in multiple stages in a series of reaction vessels if desired for optimum efficiency in the continuous mode or for product quality. Each step is preferably carried out in the absence of oxygen. The following will describe the process in terms of the preferred continuous mode.

[0011] An esterification catalyst is optional but preferred in an amount of about 5 ppm to about 100 ppm (metal), preferably about 5 ppm to about 50 ppm, based on the weight of final polymer. Because of the desirable lower temperatures under which the esterification is carried out, the esterification catalyst will be of relatively high activity and resistant to deactivation by the water byproduct of this step. The currently preferred catalysts for the esterification step are titanium and zirconium compounds. The currently preferred catalyst for esterification, prepolymerization, and polycondensation is titanium tetrabutoxide. The catalyst is preferably formulated and added to the monomer feed, prior to or during the esterification, as a dilute liquid solution in 1,3-propanediol. This catalyst feed will preferably contain 5 wt % or less titanium.

[0012] The invention 1,3-propanediol-based aromatic polyester prepared by the invention process has an intrinsic viscosity (IV) of at least 0.6, preferably 0.7 or greater, most preferably 0.8 or greater, and for some applications, preferably within the range of about 0.9 to about 1.3, as measured in a solution of 0.4 g polymer in 100 ml of a 60:40 solution of phenol:tetrachloroethane at 30° C. (or as a dilute solution in another solvent such as hexafluoroisopropanol, and converted by known correlation to the corresponding IV in 60:40 phenol:tetrachloroethane).

[0013] The first step of the process of the present invention is spinning the PTT polymer into a partially oriented yarn (POY) with an elongation at break of <160% by varying the winder take-up speed between 1,000 and 4,500 m/min.. Alternatively, the extruded filament bundle can be cooled and then drawn between a set of heated godets to a final elongation of 60 to 150%. The yarn is then wound into appropriate packages.

[0014] Yarn made with either one of the above methods is then draw-textured in a false-twist draw-texturing machine at a draw ratio of 1.02 to 1.6, preferably 1.05 to 1.4. The false-twist method is preferred for texturing into high elastic yarn for stretch fabrics because it gives higher twist density, high crimp, and latent torque energy needed for stretch yarn compared to other texturing methods such as edge-crimping and stuffer box crimping. The false-twist method is a continuous method for producing textured yarns which utilizes simultaneous drawing, twisting, heat setting, and untwisting. The yarn is taken from the supply package and fed at controlled tension through the heating unit, through a false-twist spindle or over a friction surface that is typically a stack of rotating discs called an aggregate or crossed friction belts, through a set of take-up rolls, and onto a take-up package. The twist is set into the yarn by the action of the heater tube and subsequently removed above the spindle or aggregate resulting in a group of filaments with the potential to form helical springs.

[0015] The yarn is heated to a temperature of 120 to 160° C., preferably 130 to 150° C. The goal is to make the yarn soft for drawing and twisting. If a contact heater is used, then the heater may be operated at the above temperature range. However, if a non-contact heater is used, then the heater may be operated at a higher temperature of 180 to 260° C., preferably 200 to 240° C.

[0016] The draw-textured yarn (DTY) is then subjected to a second heat set treatment before it is wound and further processed. The second heater is often part of the DTY machine but a separate heater may also be used. The second heat set is done at a lower temperature than the first heater by about 35° C. Thus the yarn is set in the second heater at 70 to 130° C., preferably 85 to 115° C. If a contact heater is used, it may be operated at this temperature range. If a non-contact heater is used, it should be operated at an appropriately higher temperature of 120 to 200, preferably between 140 to 180° C.

[0017] To finish the yarn and make a fabric, the standard steps of knitting, dyeing of fabric with disperse dyes at 100 to 110° C. without using a carrier, setting the fabric in a tentor frame with overfeed at 130 to 170° C., and finishing with a softener may be used. Some of the stretch of the yarn is lost during the finishing but when the above proper finishing parameters are used, the final fabric has good stretch and has very good hand. This is quite surprising since the conventional wisdom is that a second heat set will destroy the stretch of a polyester fabric.

EXAMPLES Example 1

[0018] PTT Fiber Extrusion Using a SDY Machine:

[0019] PTT chips (IV=0.92 dl/g) were dried in a close-loop hot air dryer at 130° C. to a final moisture level of <30 ppm. They were extruded at 254° C. into 8-end 90 denier/24 filament yarns by first cooling the filament bundles in a quench cabinet. 0.6% Delion HKS-19 (supplied by Takemoto Oil) spin finish was applied to the filament bundles prior to wrapping on a 54° C. heated godet at 2,500 m/min. The yarns were drawn with a draw ratio of 1.43 between this first heated godet and a second set of godet at 80° C. and at a speed of 3,580 m/min. They were then wound at 3,410 m/min. into 9-kg packages. Yarn Properties: Denier 84.6 Tenacity  3.13 g/den. Elongation 65% Boiling Water Shrinkage  9.2% Uster  1.2%

[0020] Draw-Texturing:

[0021] The yarns were draw-textured using a Teijin Seikki 15M friction-disc type false-twist machine with non-contact heaters for both the first heater and the second heater. Texturing Conditions: Yarn Speed 650 m/min. Draw Ratio  1.15 D/Y Ratio  2.25 OF2  2.0 OF3  4.5 First Heater: Short/Long 200/210° C. Sections Second Heater 160° C. Disc  9 mm PU disc in 1-6-1 Configuration

[0022] Textured Yarn Properties: Denier 81.5 Elongation 42% Crimp Contraction 49.0% BWS 10.0%

[0023] Knitting:

[0024] The textured-set DTY yarn was knitted with interlock circular knitting at 22 rpm using a 96- feeder, 36-inch and 24-gauge machine. The fabric weight was 230 g/yd.

[0025] Dyeing and Finishing:

[0026] The knitted fabric was dyed using disperse dye into navy blue color at atmospheric boil for 30 minutes. The fabric width before dyeing was 174 cm, and was 150.4 cm after dyeing. It was further set at 150° C. for 2 minutes in tentor frame and finished with a silicone-based softener. The final fabric width was 140.2%. Shrinkage from dyed to finished fabric was 19.4%.

[0027] Fabric Properties:

[0028] The finished fabrics had excellent hand, stretch, and recovery. This tactile property is evaluated based on touch by five-experienced textile engineers as being exceptional.

[0029] Morphology of Fabric:

[0030] The course and wale directions of the final fabric are skewed at an angle to each other instead of perpendicular to each other. There is also an out-of-plane twist of the knitted loops in the course direction. The degree of skewed angle and out-of-plane twisting of loops were dependent on the amount of crimp input from false-twisting and degree of set with second heater. The relatively ordered loop structures after dyeing and finishing also contributed to the overall excellent hand and stretch of the fabric.

Example 2

[0031] PTT Fiber Extrusion to POY Using Conventional Machine Without Heated Godet:

[0032] PTT chips (IV=0.92 dl/g) were dried in a close-loop hot air dryer at 130° C. to a final moisture level of <30 ppm. They were extruded at 258° C. into 4-end 130 denier/24 filament yarns by first cooling the filament bundles in a quench cabinet. 0.5% Lurol 7089 (supplied by Goulston) spin finish was applied to the filament bundles. Via a Duo godet the yarn was wound on a Barmag SW winder at a speed of 2800 m/min into 10 Kg packages. POY Properties: Denier 130 Tenacity  2.2 g/den. Elongation 110% Uster  1.1%

[0033] False-twist-Texturing:

[0034] The yarns were draw-textured using a Barmag AFK disc type DTY machine. (1) HE (high extensibility) yarn: Texturing Conditions Yarn Speed 600 m/min. Draw Ratio  1.52 D/Y Ratio  1.8 First Heater: Short/Long 240/220° C. Sections Disc  9 mm PU disc in 1-4-1 Configuration Second Heater (short) Off

[0035] Textured HF Yarn Properties: denier/fil 89/24 Tenacity g/den.  3.05 Elongation % 35 Crimp contraction % 48 Crimp modulus % 33 Crimp stability % 90

[0036] 2) Low Extensibility Set yarn: Texturing Conditions Yarn Speed 600 m/min. Draw Ratio  1.52 D/Y Ratio  1.8 First Heater: Short/Long 240/220° C. Sections Disc  9 mm PU disc in 1-4-1 Configuration Second Heater (short) 160° C.

[0037] Textured Set Yarn Properties: Den./fil 100/24 Tenacity g/den  3.74 Elongation %  47 Crimp contraction %  24 Crimp modulus %  9 Crimp stability %  77

[0038] Knitting:

[0039] The textured HE and set yarn were knitted with interlock circular knits at 22 rpm using a 96-feeder, 36-inch and 28-gauge machine. The fabric weights were kept constant at 260 kg/m2 by adjusting the stitch length since the low extensibility set yarn has a slightly higher denier than the high extensibility yarn.

[0040] Dyeing and Finishing:

[0041] The knitted fabrics were dyed using disperse dye into purple color at atmospheric boil for 30 minutes. Both fabrics were further set at 150° C. for 30 seconds on a tentor frame, and finished with a silicone-based softener (Ultratex ex Ciba-Geigy).

[0042] Fabric Properties:

[0043] The properties of both HE-based and set-based yarn are given in the table below. The hand (tactile property) is evaluated based on touch by five-experienced textile engineers. An independent textile laboratory (ITF, France) measured elastic performance. high extensibility yarn-based set yarn-based interlock interlock property fabric fabric 2X hysteresis cycle Stitch length (cm/100 st.) 24.4 25.2 Stitch density (st/cm²) 486 464 fabric weight Kg/m2 260 260 width E% at 10N 98 136 (length E% at 10N) 35 35 Elastic recovery 90 93 (Δ1₀ − Δ1₁)/Δ1₀ × 100% Permanent deformation % 2 2.2 Touch/Handle good superior

[0044] Unexpected Results:

[0045] Unexpectedly, the knitted fabric of example 1 using set false-twist textured yarn gave a fabric with a combination of good stretch and hand.

[0046] In Example 2, false-twist texturing was done with a controlled un-set high extensibility PTT yarn. As expected from teachings of false-twist texturing technology such as by Lubos Hes and Petr Ursiny, and Demir and Behery, the crimp contraction of PTT textured yarn decreased from 48% (high extensibility DTY) to 24% (low extensibility DTY) when it was set with a secondary heater. However, we were surprised to find that the set yarn knitted fabric had a higher stretch of 136% in the width direction than the 98% stretch of the high extensibility yarn fabric. The stretch in the length direction remained the same for the two fabrics. The elastic recovery and permanent deformation of the two fabrics were essentially similar at about 90% and 2% respectively. What was more surprising was the hand of the set yarn fabric was superior than that of the un-set high extensibility yarn fabric. These results were totally unexpected since current false-twist technology teaches that hand can only be improved at the expense of stretch. 

We claim:
 1. A process of making a stretch fabric with excellent hand from polytrimethylene terephthalate which comprise: (a) spinning a polytrimethylene terephthalate polymer into a partially oriented yarn with elongation of 60 to 150%, (b) draw-texturing the yarn in a false-twist draw-texturing machine at a draw ratio of 1.02 to 1.6, and a yarn temperature of 120 to 160° C., and (c) heat setting the draw-textured yarn at a yarn temperature of 70 to 130° C.
 2. The process of claim 1 wherein the draw-texturing temperature is from 130 to 150° C. and the second heat set temperature is from 85 to 115° C.
 3. The process of claim 1 wherein the draw-texturing is carried out at a draw ratio of from 1.05 to 1.4.
 4. A process of making a stretch fabric with excellent hand from polytrimethylene terephthalate which comprise: (a) spinning a polytrimethylene terephthalate polymer yarn and drawing it in-situ using heated godets to a final elongation of 60 to 150%, (b) draw-texturing the yarn in a false-twist draw-texturing machine at a draw ratio of 1.02 to 1.6, and a yarn temperature of 120 to 160° C., and (c) heat setting the draw-textured yarn at a yarn temperature of 70 to 130° C.
 5. The process of claim 4 wherein the draw-texturing temperature is from 130 to 150° C. and the second heat set temperature is from 85 to 115° C.
 6. The process of claim 4 wherein the draw-texturing is carried out at a draw ratio of from 1.05 to 1.4. 